According to new research, those who exercise compared with those who do not are biologically younger by up to 9 years. In the study of 2,401 twins, researchers examined their DNA as well as exercise activities. They found those exercising vigorously 3 hours each week compared with those who exercised less than 15 minutes were biologically 9 years younger. Those who exercised moderately for 1.5 hours each week were biologically 4 years younger. According to the researchers, exercise lowers the risk of a range of problems such as heart disease, cancer and diabetes. Researchers are still unclear as to why exercise has these positive effects on the body but believe it somehow may prevent oxidative stress which damages and kills cells of the body.